Rhabdomyosarcoma (RMS) is a childhood malignant tumor and is thought to arise due to the arrest of skeletal muscle differentiation (myogenesis) program. It accounts for 3.5% of all malignancies in children. Despite multimodality therapeutic treatment approaches, the outlook for patients with metastatic subtype, alveolar rhabdomyosarcoma (ARMS), remains unchanged. Moreover, conventional toxic chemotherapeutic strategies fail to succeed for the treatment of metastatic rhabdomyosarcoma; therefore, urgent need of novel approaches for the development of new pharmaceuticals to treat this dreadful disease. Because rhabdomyosarcoma cells are defective to complete myogenic terminal differentiation program, restoration of this abortive differentiation program in these cels would be a novel promising anti-RMS chemotherapeutic approach. The ultimate goal of this proposal is to develop novel approach-based new pharmaceuticals capable of restoring the differentiation block in rhabdomyosarcoma cells for the treatment of metastatic rhabdomyosarcoma. While studying the anti-muscle differentiation mechanisms in alveolar rhabdomyosarcoma (ARMS) cells, we found increased level of epigenetic modifier histone H3 lysine-9 methyltransferase Suv39H protein (referred herein KMT1A as per new nomenclature) when these cells were grown in differentiation conditions. Investigation into the mechanism of induced KMT1A expression in the arrest of ARMS cell differentiation led us a recent publication (Cancer Res. (2011) 71(11): p. 3921-31). In this study, we have demonstrated that KMT1A depletion by shRNA restores growth arrest and terminal myogenic gene expression mediated by MyoD, which acts as a key myogenic transcriptional regulator of myogenic program and universally expresses in RMS cells. Moreover, KMT1A depleted ARMS cells fail to develop tumor in vivo. Thus, we are considering KMT1A as a prospective target for developing pharmaceuticals for restoration of MyoD mediated terminal differentiation as an unconventional novel chemotherapeutic strategy for the treatment of metastatic rhabdomyosarcoma disease. The current proposal is focused on exploiting this opportunity as a first step towards developing anti- KMT1A pharmaceuticals for the treatment of ARMS. We will use functional screening of small molecule chemical libraries to identify KMT1A inhibitors capable of inducing MyoD-mediated terminal differentiation in ARMS cells. Specifically, we plan to: 1) Small molecule chemical library screening for inhibitors of KMT1A that re-activate MyoD mediated transcription. 2) Characterization of hits for their ability to suppress KMT1A mediated inhibition of MyoD-induced muscle differentiation in metastatic RMS (ARMS) cells. Completion of this proposal should identify KMT1A inhibitors capable of reprogramming MyoD mediated terminal differentiation in ARMS cells and provide a solid platform for subsequent development of KMT1A antagonist pharmaceuticals for clinical applications to treat metastatic rhabdomyosarcoma and other diseases associated with KMT1A deregulation PUBLIC HEALTH RELEVANCE: Metastatic rhabdomyosarcoma (alveolar subtype, ARMS) is incurable using current treatment strategies. Targeting the histone H3 lysine-9 methyltransferase Suv39H, which appears to block MyoD-mediated terminal myogenic program in ARMS cells, represents a novel treatment strategy for the reactivation of MyoD, a key myogenic differentiation factor, in ARMS. This approach should provide a more efficacious and less toxic alternative to current treatment strategies and, thus, has major implications for the therapeutic management of all children with this aggressive disease.